The present invention relates to the field of non-reciprocal optical devices such as optical circulators or the like.
Optical circulator devices are well known in the art and normally comprise a series of bi-directional ports and a xe2x80x9cnon-reciprocalxe2x80x9d mapping between ports. For example, in a three-port optical circulator device, the ports may be designated A, B and C and the non-reciprocal nature of the device is such that an input signal at Port A will be output at Port B, an input signal at Port B will be output at Port C and an input signal at Port C will be output at Port A.
It is desirable with any circulator type device to manufacture as compact and inexpensive a device as possible.
The object of the present invention is to provide for a compact form of optical circulator device having a high level of compactness and flexibility.
In accordance with a first aspect of the present invention, there is provided a non-reciprocal optical device mapping a series of optical input/output signal waveguides to a corresponding series of optical input/output signal waveguides, the device comprising: a series of spaced apart input/output waveguides; a reflective imaging system for reflecting and focussing light emitted from the input/output waveguides; a plurality of crystal elements between the input/output waveguides and the reflective imaging means; at least one non-reciprocal polarization rotation element; wherein light emitted from a first input/output waveguide is transmitted to a second input/output waveguide in a polarization independent manner and light emitted from the second input/output waveguide is transmitted away from the first input/output waveguide.
Light emitted from the second input/output waveguide can be transmitted to a third input/output waveguide and light emitted from the third input/output waveguide can be transmitted to the first input/output waveguide so as to provide for a fully circulating circulator.
The input/output signal waveguides can comprise optical fibres and mode expansion can be provided by utilizing thermally expanded core fibre ends, gradient index fibres, or a separate lensing system, or a combination of thereof.
In accordance with a further aspect of the present invention, there is provided a non-reciprocal optical device mapping a series of optical input/output signal waveguides to a series of optical input/output waveguides, the device comprising: a series of spaced apart input/output signal waveguides; a first polarization separation means for spatially separating the optical input signals emitted from the optical input/output signal waveguides into orthogonal polarization components; a first series of reciprocal polarization transformation elements for aligning the polarizations thereby producing aligned polarization components; a non-reciprocal rotator for applying a non-reciprocal rotation to the aligned polarization components; a second polarization separation means for spatially displacing aligned polarization components; at least one reciprocal polarization transformation element for rotating the aligned polarization components emitted from a subset of the input/output signal waveguides; imaging means for imaging the aligned polarization components to produce imaged polarization components; and reflection means for reflecting the polarization components wherein light emitted from a first input/output waveguide is transmitted to a second input/output waveguide in a polarization independent manner and light emitted from the second input/output waveguide is transmitted away from the first input/output waveguide.
Again, light emitted from the second input/output waveguide can be transmitted to a third input/output waveguide and light emitted from the third input/output waveguide can be transmitted to the first input/output waveguide so as to provide for a fully circulating circulator.
In accordance with a further aspect of the present invention, there is provided a non-reciprocal optical device comprising: at least two spaced apart rows each containing a series of input/output waveguides; a first polarization dependant displacement means spatially displacing orthogonal polarizations of light emitted from the waveguides; a first series of reciprocal polarization transformation elements aligning the orthogonal polarizations emitted from the first polarization displacement means; a non reciprocal-rotator rotating the aligned polarization states in a non reciprocal manner; a second polarization dependant displacement means displacing light emitted from the reciprocal polarization transformation element in a polarization dependant manner; focusing means for focusing light emitted from the waveguides substantially on the waveguides; reflection means reflecting light emitted from a first of the rows back in the direction of a second of the rows; wherein light emitted from a first one of the waveguides in a first row is transmitted to a first one of the waveguides in a second row in a non reciprocal manner.
The light emitted from the first one of the waveguides in the second row is preferably transmitted to a second one of the waveguides in the first row.
In one embodiment, the number of waveguides in each row can be four and light emitted from any one of the waveguides in a first row can be transmitted to a predetermined waveguide in the second row. The first polarization means preferably translates one orthogonal polarization state substantially perpendicular to the rows.
The first series of reciprocal polarization transformation elements can comprise a series of abutted reciprocal rotators which rotate the displaced orthogonal polarizations in an opposite direction. The focusing means can be adjacent the reflection means. The second polarization displacement means can displace one of the polarizations parallel to the rows.
In accordance with a further aspect of the present invention, there is provided a method of mapping a first series of optical input/output signal waveguides to a second series of optical input/output waveguides in a non-reciprocal manner, the method comprising the steps of: (a) emitting an optical signal from one of the waveguides; (b) spatially separating substantially orthogonal polarisation states of the emitted light using a first optical element; (c) aligning the substantially orthogonal polarization states using a second optical element; (d) projecting the aligned orthogonal polarization states through a first series of optical elements; and (e) reflecting the light emitted from the step (d) back through the first series of optical elements, the second optical element and the first optical element; wherein light emitted from the first one of the waveguides is transmitted to a second one of the waveguides and light emitted from a second one of the waveguides is transmitted to a third one of the waveguides.
The light is ideally transmitted from one waveguide to a second in a polarization independant manner and light emitted from the third one of the waveguides can be transmitted to the first waveguide.
Many different uses of the circulator are possible. For example, an add/drop multiplexer or other optical transmission system.